We propose a dynamic model for the copolymerization of alpha-methyl styrene (alpha-MS) and methyl methacrylate (MMA) in a batch reactor. The parameters are based on data from the literature and our own laboratories over the full conversion range. A two-parameter model with constant reactivity ratios shows the most reasonable results. The dynamic model depicts the reaction kinetics and reactor behavior more clearly. Termination occurs mainly by the cross reaction of unlike radicals, and its rate increases with the molar ratio of alpha-MS to MMA. The model enables us to predict the instantaneous and cumulative properties of the copolymer and also provides us with a basic tool for the optimization and control of industrial reactors. (C) 2004 Wiley Periodicals, Inc.